Dismantling work begins on the south facade of the Mackintosh building in Glasgow.
Photograph: Jeremy Sutton-Hibbert for the Guardian

Glasgow School of Art’s Mackintosh building, which was gutted by fire last month, will be rebuilt, the school’s director has told the Guardian.

The commitment by Tom Inns ends weeks of speculation about the fate of the 110-year-old building, after many experts raised fears that the scale of the blaze would make it impossible to rescue and rebuild it.

In his first interview since the fire, Inns said: “We’re going to rebuild the Mackintosh building. There’s been a huge amount of speculation about what should happen with the site and quite rightly so, but from our point of view and that of the city of Glasgow, it is critically important that the building comes back as the Mackintosh building.”

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Acknowledging the “anger and frustration” felt by many, Inns said he was confident that the many questions raised about how the building could have suffered another devastating fire, after a previous blaze in 2014, would be answered by an ongoing investigation by the Scottish fire and rescue service, and he said the rebuild costs would be covered by insurers.

He also said assurances from Kier Construction, the contractors overseeing the Mackintosh restoration after the 2014 fire, that an adequate fire safety strategy was in place had been “professionally checked” by the art school.

A third of the Mackintosh, including its internationally renowned library, sustained significant damage in the first fire, and the building was due to reopen next year after a £35m restoration. But the work was all but destroyed by the latest fire, although Inns confirmed that around half of the library’s fixtures and fittings, many of which had been restored from fragments, were in storage at the time of June’s blaze.

Concerns had been raised that the exterior stonework of the building, which had already been weakened by the intense heat of the first fire and then its rapid cooling when the flames were doused, would not survive the second blaze.

Inns said it was impossible to know how much of the remaining structure would be reusable until work had been completed to dismantle those sections of the building, including a large part of the south-east and west facades that are dangerously unstable.

That process began on Tuesday afternoon, with brickwork and masonry being taken down manually in a highly controlled exercise using a crane hoist and elevated platforms to ensure minimum danger to surrounding property.

Inns said that thanks to detailed digital modelling carried out as part of the restoration work, specialists had “incredible insight into every corner of that building”, which had helped to speed up the dismantling plans.

The building was badly damaged in a fire on the night of Friday 15 June. Photograph: Jeff J Mitchell/Getty Images

Those in favour of bulldozing the site and conceiving an entirely new building have argued that replicating the Mackintosh piece by piece would turn the school into a museum piece. But Inns said the intention was for the building to reopen as a working part of the art school campus. “To have the Mack building you have to have the building and you have to have the space inside it, the creative education.”

Other experts have looked to Germany’s postwar experience, in particular the Neues Museum, which combines a respectful restoration with imaginative new additions. But Sally Stewart, the school’s head of architecture, pointed to the difficulties of disturbing the building’s delicate internal ratios.

“The beauty of the Mack was that in its design it really considered the internal environment needed for the disciplines that were housed in it. In terms of the light within the studios, how the studios were scaled, to tinker with any of that is really tricky.”

Since the second fire, a number of questions have been raised about the adequacy of the fire safety precautions put in place by Kier Construction, after it emerged that a new sprinkler system had not yet been fitted. Kier, which has said it had an agreed fire safety strategy in place, has now concluded its relationship with the art school.

Inns was unable to discuss specific concerns while the fire service investigation was ongoing, but he said: “We’re really clear in our minds that we had assurances from our contractor about what was in place on that site and that it totally fulfilled all the requirements [for fire safety].”

Inns also said: “The building is insured and we’re confident that we can rebuild the building based on that.” He said it was too early to say whether further fundraising would be required – Brad Pitt led a star-studded appeal with a target of £32m after the 2014 fire – but he added: “At the moment we’re not requesting support from either government [Scottish or UK].”

He said he was confident there would be a comprehensive investigation by Scottish fire and rescue. “I think that will answer a lot of the speculation about what’s actually happened.”

Referring to calls for a public inquiry into the second fire, he said it was “something for those that put those inquiries in place to decide”, and the art school would “collaborate closely” with any further investigation.